Your units can also gain experience points and have their ranks increased which boosts their attack power. (gearnuke.com)
This is an excellent comeback mechanic that temporarily boosts your attack power, health recovery and combo capabilities, and lasts longer the fewer fighters you have left on your side. (tomsguide.com)
Sure, they can just boost your attack power or whatever, but the article on these new additions makes it clear that flat bonuses are the least of what you can get. (massivelyop.com)